Grinder for rubber sleeves

ABSTRACT

A device for grinding rubber from tubular sleeves mounted on a turret which is rotatable for positioning the sleeves adjacent a belt sander which is also rotatable into and out of sanding or buffing relation with a rubber sleeve positioned closest the sander.

o United States Patent 11 1 1 1111 3,745,728 Boehm, Sr. July 17, 1973 GRINDER FOR RUBBER SLEEVES 2,6l2 007 9 1952 BC" 51 145 T 1 1 Inventor Karl 809m, 819M101, Ohio 5:223:35 3/133 232E323": 311751715 515 7 Th G 2,405,417 8/1946 P111111 51/145 T Sslgnea .nlff'zfgg & Rubber Com 2,352,690 7 1944 Clausing... 51 145 T p 3,534,502 10/1970 Lovely 51 290 x 22 Filed: "Sept; 1971 I 1 7 1 Primary Examiner-Donald G. Kelly 1 Appl' 185017 Attorney-F. W. Brunner et al.

[52] U.S. Cl... 51/145 T, 51/105 R, 51/215 AR [57] ABSTRACT [51] '3" B241) 21/02 B24b 21/181 B24b 41/04 A device for grinding rubber from tubular sleeves [58] Fleld of Search 51/ l45 T, R, mounted on a turret which is rotatabk for positioning 51/215 215 32 the sleeves adjacent a belt sander which is also rotatable into and out of sanding or buffing relation with a [56] References Cited 7 STATES PATENTS 140,732 7/1873 -R6us6...;;; .;.....-5l/145T rubber sleeve positioned closest the sander.

24 Claims,v 2 Drawing Figures PAIENTEU JUL 1 1 I975 SHEEI 1 0F 2 PATENTEQJUL 1 7 I975 SHEET 2 [IF 2 GRINDER FOR RUBBER SLEEVES BACKGROUND OF THE INVENTION The invention is particularly useful for buffing or grinding rubber sleeves used in connection with shock absorbers. Such sleeves are conventionally molded. However, it is difficult to precisely mold these sleeves and usually they must be buffed to remove excessive rubber, if the sleeves are to accurately fit adjacent parts of the shock absorber. Normally, the sleeves are individually ground using an abrasive grinding wheel. The invention is directed to a machine for automatically grinding a number of sleeves which are successively positioned and buffed by a highly improved grinding device.

Briefly stated, the invention is in a machine for sanding, buffing, or grinding hollow tubular members. The machine comprises a turret which is rotatable about a fixed axis. A number of spindles or mandrels, for receiving and holding the members, extend in parallel relation from the turret and are equally distant from, and equally spaced angularly about, the rotational axis of the turret. The mandrels are each mounted for rotation about an axis which is parallel to the rotational axis of the turret. An abrasive surface for engaging a member positioned on a mandrel closest the surface, is moved in a partially circular pathway about an axis parallel to the rotational axis of the turret. The mandrel holding the member being ground, is simultaneously rotated in the same rotational direction that the abrasive surface moves about its axis of rotation. The abrasive surface is moved into and out of grinding engagement with the member held inposition closest the moving surface. Moreover, the movement of the abrasive surface is synchronized with rotation of the turret such that after grinding a member, the abrasive surface moves away from the member until the turret is rotated and the next in line member is moved into position for engagement with the abrasive surface.

DESCRIPTION OF THE DRAWING The following description of the invention will be better understood by having reference to the annexed drawing, wherein:

FIG. 1 is a plan view of a machine made in accordance with the invention, portions of the machine being removed to expose certain features of the machine; and

FIG. 2 is a side view of the machine.

DESCRIPTION OF THE INVENTION Referring generally to the drawing, there is shown a machine, generally indicated at 9, for grinding hollow rubber sleeves used in connection with shock absorbers. The machine 9 comprises a turret assembly 1 l and a grinder assembly 12 disposed in side-by-side relation on a table top 13 of a machine stand or frame 14. Turret Assembly 7 The turret assembly 11 comprises a standard rotary indexing table or turret 15, as manufactured by Bellows-Valvair Company located in Akron, Ohio. The turret 15 is mounted for rotation about a fixed axis which is parallel to the table top 13. The turret 15 comprises a circular plate 16 which lies in a plane normal to the rotational axis of the turret 15. The plate 16 is supported on a pair of spaced rollers 17 and 18 which are, in turn, rotatably mounted on a pair of brackets l9 and 20 secured to the table top 13. An air cylinder 21 is coupled to the turret 15 for rotating the plate 16.

A number of spindles or mandrels 22-33 are journalled in the plate 16 for rotation about axes which are parallel to the rotational axis of the turret 15. The mandrels 22-33 are equally distant from, and equally spaced about, the rotational axis of the turret 15.

A standard helical gear 34 is secured to a reduced end section 35 of each of the mandrels 22-33 for unitary rotation with the mandrels. The helical gears 34 are in aligned, planar relation and are designed for meshing engagement with a mating helical drive gear 36 which is rotated by a conventional air motor 37 mounted adjacent the grinder assembly 12.

Each of the mandrels 22-33 has an outer cylindrical periphery 38, a plurality of openings 39 disposed in the periphery 38, a center bore 40 and a plurality of similar air passageways 41 connecting the openings 39 and center bore 40.

A number of air nozzles 44, 45, and 46 (hidden from view) are carried by a nozzle holder 47 which is disposed adjacent the plate 16. An air cylinder 48 is coupled to the nozzle holder 47 and used for reciprocating the air nozzles 44, 45, and 46 into and out of communication with the center bores 40 of adjacent mandrels 27-29. A conventional air pressure system (not shown) is coupled to the air nozzles 44, 45, and 46 for forcing air, under pressure, through the openings 39 to facilitate removal of buffed rubber sleeves from the man drels and replacement with unbufied sleeves. A conventional limit switch 49 is supplied for limiting movement of the nozzles 44-46 towards the ends of adjacent mandrels 27-29.

A shot-pin locater 53 is disposed adjacent a mandrel, e.g. mandrel 22, with a sleeve 10 in position for grinding or buffing. The shot-pin locater 53 comprises an air cylinder 54 for reciprocating a pin 55 into and out of engagement with a cantilevered end 56 of the mandrel 22 positioned for meshing engagement with the helical drive gear 36. Thus, the mandrel 22 and surrounding rubber sleeve 10 are rigidly supported to insure accurately buffing sleeve 10 throughout its length.

Grinder Assembly The grinder assembly 12 comprises a bed 60 which is pivotally mounted, intermediate its opposing ends 61 and 62, to the machine stand 14. The bed 60 rotates or rocks in a plane normal to the rotational axis of the turret 15 and about an axis which is parallel to said rotational axis. A block 63 and support bracket 64 are secured on the bed 60 adjacent the ends 62 and 61, respectively. A cam follower, e.g. roller 65, extends downwardly from the bed 60 in opposed relation from the support bracket 64.

A base 66 is slidably keyed to the block 63 and rests on the support bracket 64. A hand crank 67, rotatably coupled to the base'66 and threadably engaging the support bracket 64, is utilized for adjusting the position of the base 66 relative to the pivot A about which the bed 60 rocks, i.e. rotation of the hand crank 67 causes movement of the base 66 in a direction towards and away from the adjacent turret assembly 11. A hand nut 68 and bolt 69 are provided for firmly securing the base 66 to the support bracket 64. An electric motor 70 is bolted on the base 66 and used for driving a belt sander, generally indicated at 71.

The belt sander 71 comprises a front drive pulley 72 and a rear idler pulley 73 disposed in spaced relation on the base 66. The pulleys 72 and 73 are mounted for rotation about axes which are parallel to the rotational axis of the turret 15. The position of the front drive pulley 72 on the base 66 is fixed, whereas the rear pulley 73 is movable relative to the front pulley 72. The rear pulley 73 is rotatably mounted on a link arm 74 which is pivotally mounted on a pivot bracket 75 secured in upstanding relation on the base 66. An air cylinder 76 is coupled to the link arm 74 and used for rotating the rear pulley 73 about the pivot B, whereby the rear pulley 73 is reciprocated towards and away from the front drive pulley 72. A belt 77 which, in this case, is a continuous loop of sandpaper with an abrasive surface, is looped or reeved around the front drive pulley 72 and rear pulley 73. The electric motor 70 is coupled by a drive belt 78 to the front drive pulley 72. A housing 79 is supplied for partially enclosing the belt sander 71. A flexible hose 80 is secured to the housing 79 adjacent the front drive pulley 72 for removing particles of rubber buffed or ground from the sleeves. An adjusting screw 81 is provided for aligning the rear pulley 73 with the front drive pulley 72.

An electric motor 85, including a rotatable shaft 86, is mounted on the machine stand 14 beneath the table top 13. A cam 87 is keyed for unitary rotation with the motor shaft 86. The cam 87 may be a circular disc which is eccentrically mounted on the motor shaft 86. However, movement of the belt sander 71 is more accurately controlled by a specially designed cam 87, including an arcuate projecting segment 88 and a circular segment 89. The cam follower 65 rides along these surfaces 88 and 89 as the cam 87 rotates. The helical drive gear 35 rotates an engaged mandrel in the same rotational direction as the front drive pulley 72 rotates to facilitate uniform grinding of the outer exposed periphery of the rubber sleeve. The rotation of the cam 87 is in synchronized timed relation with rotation of the turret 15, as will hereinafter be explained.

Operation of the Apparatus Assuming that the machine 9 is in a normally rest position, as shown in FIG. 2 where one of the mandrels 22 and surrounding sleeve is in position for grinding and the front drive pulley 72 is in farthest spaced relation from the mandrel 22, separate button switches are pressed for starting the motors 70 and 85 controlling operation of the belt sander 71 and cam 87. The cam 87 begins rotating, as shown, and the cam follower 65 moves from the circular segment 89 on to the projecting portion 89 of the cam 87. This causes rotation of the bed 60, base 66, and belt sander 71 about the pivot A, whereby the belt sander 71 is moved into grinding relation with the rubber sleeve 10 on the adjacent mandrcl 22.

The base 66, in its rest position, is in contact with a normally closed switch 91 and a normally open switch 92. As the bed rotates, the normally closed switch 91 opens and the normally open switch 92 closes. The switch 92, as it closes, operates the following mechanisms in timed sequence. The air cylinder 54 of the shot-pin locater 53 is actuated to move the pin 55 into supporting relation with the adjacent free cantilevered end 56 of the mandrel 22. Shortly thereafter and prior to the belt sanders 7l engaging the rubber sleeve 10, the air motor 36 is actuated for rotating the helical drive gear 35 which is in meshing engagement with the helical gear 34 carried by the mandrel 22. Thus, the mandrel 22 is rotated in the same rotational direction that the front drive pulley 72 is being rotated. Almost simultaneously with operation of the air motor 36, the air cylinder 48 is actuated to move the plate 47 and attached air nozzles 44-46 into air communication with the centerbores 40 of adjacent mandrels 27-29.

The belt sander 71 grinds rubber from the adjacent sleeve 10 for a predetermined period of time in correlated relation to the speed of rotation of the cam 87. For example, the cam 87 is designed such that the belt sander 71 will remove within one-thousandth of an inch of rubber from the adjacent sleeve. Thus, it can be appreciated that the sleeves can be sanded or buffed with machine-like precision.

The belt sander 71 is rotated back to its rest position as the cam follower moves off the projection back on to the circular segment 89 of the cam 87, and the closed switch 92 is reopened. Accordingly, the air cylinder 48 controlling operation of the air nozzles 44-46, the air motor 36 controlling rotation of the mandrel 21, and the air cylinder 54 of the shot-pin locater 53 are deactuated in timedsequence to either stop operation of the various components involved, or move the components back to their rest positions, as previously described. The normally closed switch 91, which has been open, is again closed and actuates the air cylinder 21 for rotating the indexing table or turret 15 such that the next succeeding mandrel 23 and associated sleeve are moved into buffing position closest the front drive pulley 72 of the belt sander 71.

As the turret 15 rotates, a previously bufied sleeve on one of the mandrels, e.g. mandrel 31, engages a sensor 93 in electrical communication with a gauge 94 (schematically represented) which indicates whether suffcient rubber has been removed from the sleeve. If, for example, the measurement falls within prescribed limits, a green liglit 95 lights up. Otherwise, a red light 96 flashes and the machine 9 is automatically shut down until the operator can determine the problem as to why the sleeves are not being properly ground. Once the problem has been located and corrected, the machine 9 can be reactivated.

The turret assembly 11 and grinder assembly 12 are synchronized to operate in timed sequence, whereby the mandrels 22-33 are successively moved into grinding position, and the belt grinder 71 is rotated into buffing relation with the sleeve on the properly positioned mandrel. The position of the belt sander 71 in relation to the pivot A can be adjusted such that the belt sander 71 will remove more or less rubber from the sleeve it is grinding.

It has been found more desirable to use a belt sander rather than a conventional grinding wheel, because the wheel must be periodically removed and the surface of the grinding wheel redressed to remove the rubber particles which load up the surface of the wheel. It has been found that the movement and vibration of the sandpaper or emery cloth which is used on the belt sander 71 helps keep the abrasive surface of the paper or cloth relatively free from rubber particles. Thus, the belt sander is self-cleaning. Moreover, the belt of the sander is easily removed and replaced and the machine does not have to be reset when a new belt is positioned on the machine, as is normally the case when a regular abrasive grinding wheel is used.

Thus, there has been provided a highly improved apparatus for accurately grinding a number of rubber sleeves which are successively positioned in timed sequence with operation of a belt sander used for grinding rubber from the sleeves. The apparatus is automatic and designed to speed up the rate at which rubber sleeves are gound or buffed.

What is claimed is:

1. A machine for grinding tubular members comprising in combination:

a. a turret rotatable about a fixed axis;

b. a pluralityof mandrels extending in parallel relation from the turret for holding tubular members, the mandrels being equally distant from,- and equally angularly spaced about, the rotational axis of the turret;

0. means for mounting each mandrel for rotation about an axis parallel to the rotational axis of the turret; I

d. an abrasive surface for grinding a tubular member when the mandrel holding the member is in a predetermined angular position relative to the rotational axis of the turret;

e. means for rotating a mandrel when it is in said predete'rminedangular position;

f. means for moving the abrasive surface into grinding engagement with a tubular member held by a mandrel in said predetermined angular position;

g. means for cantilevering the mandrels from the tur- .ret; and

h. means for supporting the free cantilevered end of a mandrel when the mandrel is in said predetermined angular position.

2. The machine of claim 1, wherein the means for supporting the free cantilevered end of a mandrel includes: a pin for engaging said end; means for supporting the pin adjacent said end; and means for reciprocating the pin in and out of supporting engagement with said end.

3. The machine of claim 1, which includes: an outer cylindrical surface on each mandrel; a plurality of openings disposed in the surface of each mandrel; and means for forcing air, under pressure, from the openings of a mandrel when the mandrel is in a second predetermined angular position, relative to the rotational axis of the turret, and angularly spaced from said other position, said air facilitating removal of tubular members from the mandrels.

4. The machine of claim 3, wherein the means for forcing air, under pressure, from the openings includes: a bore axially disposed in each mandrel; air passageways connecting the bore and openings; at least one air nozzle disposed adjacent the turret; and means for reciprocating the air nozzle in and out of air communicating relation with the bore of a mandrel when the mandrel is in said second position.

5.'The machine of claim 3, which includes: at least one pair of spaced pulleys; means for mounting the pulleys for rotation about axes parallel to the rotational 'axis of the turret; a belt, including said abrasive surface,

reeved on the pulleys, said belt and pulleys forming a belt sander; and means for driving at least one of the pulleys.

6'. The machine of claim 5, wherein the means (f) includes: means for reciprocating the pulley, closest the mandrel in said predetermined angular position, through a limited arc towards and away from the mandrel in said position.

7. The machine of claim 6, which includes: means for mounting the belt sander on a bed; and means for rocking the bed and belt sander about a pivot intermediate opposing ends of the bed.

8. The machine of claim 7, wherein the bed rocking means includes: a cam eccentrically mounted for rotation about an axis; and a cam follower carried by the bed for rolling engagement on the cam;

9. The machine of Claim 8, wherein the bed rocking means includes: means for rocking the bed and maintaining the turret in a fixed angular position as the cam rotates through a first angle; and means for rotating the turret and maintaining the bed in a fixed position as the cam rotates through a second angle which is in succeeding angular relation to the first angle.

10. The machine of claim 8, which includes: means for adjusting the position of the belt sander on the bed in relation to the turret.

11. The machine of claim l0,which includes: means for measuring the wall thickness of a tubular-member after it is buffed.

12. The machine of claim 11, which includes: means for rotating the turret in timed sequence relation to movement of the belt sander out of buffing relation with a sleeve held by a mandrel in said predetermined angular position.

13. A machine forgrinding tubular members, comprising in combination:

a. a belt sander including, a pair of. rotatable pulleys in spaced relation, and a continuous belt with an abrasive surface looped around the pulleys;

b. a plurality of cylindrical mandrels for receiving and holding tubular members;

c. means for successively moving the mandrels to a position adjacent the belt sander;

d. means for mounting the mandrels for rotating about axes parallel to the rotational axis of the pulley closest a mandrel in said position;

e. means for rotating a mandrel when it is in said position, the rotation of the mandrel being in the same direction as the closest pulley rotates;

f. means for moving the belt sander towards a mandrel in said position such that the abrasive surface of the belt engages the tubular member on the mandrel; and

g. means for rotatably supporting opposing ends of each mandrel in said position.

14. The machine of claim 13, wherein the belt moving means (f) includes: a bed on which the belt sander is mounted; and means for rocking the bed in a plane normal to the rotational axis of a mandrel in said position.

15. The machine of claim 14, wherein the bed rocking means includes: means for mounting the bed for rotation about a pivot intermediate opposing ends of the bed; and means for reciprocating the bed and belt sander through a predetermined arc in corresponding relation to the spacing desired between a mandrel in said position and the closest pulley.

16. The machine of claim 15, wherein the means for reciprocating the bed and-belt sander includes: an eccentrically mounted cam rotatable about a fixed axis; a cam follower for riding engagement on the cam; and means for rotating the cam.

17. The machine of claim 16, wherein the belt mov ing means (c) includes: mounting the mandrels on a turret which is rotatable about a fixed axis, the mandrels being equally distant from, and equally angularly spaced around, the rotational axis of the turret.

18. The machine of claim 17, which includes: means for rotating the turret to a new angular position when the belt sander rotates to a position in farthest spaced relation from a mandrel in said position.

19. The machine of claim 18, which includes: means for mounting the mandrels in cantilevered relation from the turret; a pin disposed in supported relation adjacent a mandrel in said position; and means for reciprocating the pin into and out of supporting engagement with the adjacent free cantilevered end of a mandrel in said position.

20. The machine of claim 19, which includes: a bore axially disposed in each mandrel; a plurality of openings disposed in the outer cylindrical surface of each mandrel; an air passageway connecting the bore of each opening of a mandrel, at least one air nozzle positioned adjacent the turret, means for reciprocating the nozzle into and out of the bore of the closest mandrel when the turret is not rotating; and means for forcing 21. The machine of claim 20, which includes means for measuring the thickness of a tubular wall after buffmg.

22. The machine of claim 21, wherein rotation of the turret and belt sander are in timed sequence; and the movement of the pin and air nozzle and the rotation of a mandrel in said position, are in timed sequence to rocking of the bed.

23. The machine of claim 1, wherein the belt moving means (f) includes means for rotating the abrasive surface at least partially around an axis which is reciprocable through a limited are about a fixed pivot.

24. The machine of claim 23, which includes: means for adjusting the distance between the fixed pivot and axis about which the abrasive surface at least partially rotates, whereby the correlated spacing between the surface and adjacent mandrel in said predetermined angular position is varied.

* a: a: a:

po-wso Pmmem No. 3 7 728 Da'wd July 79 1973 Imvomzoflo) Karl W, Boel lmg SI it 11o cortified that arrow appears in the above-ideutifiefi patent and Hawk mid Letters Pammt are homby correctod as shown below:

5 Claim 17, line 1, "belt moving means should read I:

-- mandrel moving'means Signed and sealed this 20th day of November 1973 (SEAL) Attest:

EDWARD MmL'ETcBE'mJR. RENE 1);, TEGTD IEYER Attesting Officer Acting Commissioner of Patents 

1. A machine for grinding tubular members comprising in combination: a. a turret rotatable about a fixed axis; b. a plurality of mandrels extending in parallel relation from the turret for holding tubular members, the mandrels being equally distant from, and equally angularly spaced about, the rotational axis of the turret; c. means for mounting each mandrel for rotation about an axis parallel to the rotational axis of the turret; d. an abrasive surface for grinding a tubular member when the mandrel holding the member is in a predetermined angular position relative to the rotational axis of the turret; e. means for rotating a mandrel when it is in said predetermined angular position; f. means for moving the abrasive surface into grinding engagement with a tubular member held by a mandrel in said predetermined angular position; g. means for cantilevering the mandrels from the turret; and h. means for supporting the free cantilevered end of a mandrel when the mandrel is in said predetermined angular position.
 2. The machine of claim 1, wherein the means for supporting the free cantilevered end of a mandrel includes: a pin for engaging said end; means for Supporting the pin adjacent said end; and means for reciprocating the pin in and out of supporting engagement with said end.
 3. The machine of claim 1, which includes: an outer cylindrical surface on each mandrel; a plurality of openings disposed in the surface of each mandrel; and means for forcing air, under pressure, from the openings of a mandrel when the mandrel is in a second predetermined angular position, relative to the rotational axis of the turret, and angularly spaced from said other position, said air facilitating removal of tubular members from the mandrels.
 4. The machine of claim 3, wherein the means for forcing air, under pressure, from the openings includes: a bore axially disposed in each mandrel; air passageways connecting the bore and openings; at least one air nozzle disposed adjacent the turret; and means for reciprocating the air nozzle in and out of air communicating relation with the bore of a mandrel when the mandrel is in said second position.
 5. The machine of claim 3, which includes: at least one pair of spaced pulleys; means for mounting the pulleys for rotation about axes parallel to the rotational axis of the turret; a belt, including said abrasive surface, reeved on the pulleys, said belt and pulleys forming a belt sander; and means for driving at least one of the pulleys.
 6. The machine of claim 5, wherein the means (f) includes: means for reciprocating the pulley, closest the mandrel in said predetermined angular position, through a limited arc towards and away from the mandrel in said position.
 7. The machine of claim 6, which includes: means for mounting the belt sander on a bed; and means for rocking the bed and belt sander about a pivot intermediate opposing ends of the bed.
 8. The machine of claim 7, wherein the bed rocking means includes: a cam eccentrically mounted for rotation about an axis; and a cam follower carried by the bed for rolling engagement on the cam.
 9. The machine of Claim 8, wherein the bed rocking means includes: means for rocking the bed and maintaining the turret in a fixed angular position as the cam rotates through a first angle; and means for rotating the turret and maintaining the bed in a fixed position as the cam rotates through a second angle which is in succeeding angular relation to the first angle.
 10. The machine of claim 8, which includes: means for adjusting the position of the belt sander on the bed in relation to the turret.
 11. The machine of claim 10, which includes: means for measuring the wall thickness of a tubular member after it is buffed.
 12. The machine of claim 11, which includes: means for rotating the turret in timed sequence relation to movement of the belt sander out of buffing relation with a sleeve held by a mandrel in said predetermined angular position.
 13. A machine for grinding tubular members, comprising in combination: a. a belt sander including, a pair of rotatable pulleys in spaced relation, and a continuous belt with an abrasive surface looped around the pulleys; b. a plurality of cylindrical mandrels for receiving and holding tubular members; c. means for successively moving the mandrels to a position adjacent the belt sander; d. means for mounting the mandrels for rotating about axes parallel to the rotational axis of the pulley closest a mandrel in said position; e. means for rotating a mandrel when it is in said position, the rotation of the mandrel being in the same direction as the closest pulley rotates; f. means for moving the belt sander towards a mandrel in said position such that the abrasive surface of the belt engages the tubular member on the mandrel; and g. means for rotatably supporting opposing ends of each mandrel in said position.
 14. The machine of claim 13, wherein the belt moving means (f) includes: a bed on which the belt sander is mounted; and means for rocking the bed in a plane normal to the rotational axis of a mandrel in said position.
 15. The machine of claim 14, wherein The bed rocking means includes: means for mounting the bed for rotation about a pivot intermediate opposing ends of the bed; and means for reciprocating the bed and belt sander through a predetermined arc in corresponding relation to the spacing desired between a mandrel in said position and the closest pulley.
 16. The machine of claim 15, wherein the means for reciprocating the bed and belt sander includes: an eccentrically mounted cam rotatable about a fixed axis; a cam follower for riding engagement on the cam; and means for rotating the cam.
 17. The machine of claim 16, wherein the belt moving means (c) includes: mounting the mandrels on a turret which is rotatable about a fixed axis, the mandrels being equally distant from, and equally angularly spaced around, the rotational axis of the turret.
 18. The machine of claim 17, which includes: means for rotating the turret to a new angular position when the belt sander rotates to a position in farthest spaced relation from a mandrel in said position.
 19. The machine of claim 18, which includes: means for mounting the mandrels in cantilevered relation from the turret; a pin disposed in supported relation adjacent a mandrel in said position; and means for reciprocating the pin into and out of supporting engagement with the adjacent free cantilevered end of a mandrel in said position.
 20. The machine of claim 19, which includes: a bore axially disposed in each mandrel; a plurality of openings disposed in the outer cylindrical surface of each mandrel; an air passageway connecting the bore of each opening of a mandrel, at least one air nozzle positioned adjacent the turret, means for reciprocating the nozzle into and out of the bore of the closest mandrel when the turret is not rotating; and means for forcing air through the nozzle when engaged in a bore.
 21. The machine of claim 20, which includes means for measuring the thickness of a tubular wall after buffing.
 22. The machine of claim 21, wherein rotation of the turret and belt sander are in timed sequence; and the movement of the pin and air nozzle and the rotation of a mandrel in said position, are in timed sequence to rocking of the bed.
 23. The machine of claim 1, wherein the belt moving means (f) includes means for rotating the abrasive surface at least partially around an axis which is reciprocable through a limited arc about a fixed pivot.
 24. The machine of claim 23, which includes: means for adjusting the distance between the fixed pivot and axis about which the abrasive surface at least partially rotates, whereby the correlated spacing between the surface and adjacent mandrel in said predetermined angular position is varied. 